| //! Candidate assembly. |
| //! |
| //! The selection process begins by examining all in-scope impls, |
| //! caller obligations, and so forth and assembling a list of |
| //! candidates. See the [rustc dev guide] for more details. |
| //! |
| //! [rustc dev guide]:https://rustc-dev-guide.rust-lang.org/traits/resolution.html#candidate-assembly |
| use rustc_hir as hir; |
| use rustc_infer::traits::{Obligation, SelectionError, TraitObligation}; |
| use rustc_middle::ty::{self, TypeFoldable}; |
| use rustc_target::spec::abi::Abi; |
| |
| use crate::traits::{util, SelectionResult}; |
| |
| use super::BuiltinImplConditions; |
| use super::SelectionCandidate::{self, *}; |
| use super::{SelectionCandidateSet, SelectionContext, TraitObligationStack}; |
| |
| impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> { |
| pub(super) fn candidate_from_obligation<'o>( |
| &mut self, |
| stack: &TraitObligationStack<'o, 'tcx>, |
| ) -> SelectionResult<'tcx, SelectionCandidate<'tcx>> { |
| // Watch out for overflow. This intentionally bypasses (and does |
| // not update) the cache. |
| self.check_recursion_limit(&stack.obligation, &stack.obligation)?; |
| |
| // Check the cache. Note that we freshen the trait-ref |
| // separately rather than using `stack.fresh_trait_ref` -- |
| // this is because we want the unbound variables to be |
| // replaced with fresh types starting from index 0. |
| let cache_fresh_trait_pred = self.infcx.freshen(stack.obligation.predicate); |
| debug!( |
| "candidate_from_obligation(cache_fresh_trait_pred={:?}, obligation={:?})", |
| cache_fresh_trait_pred, stack |
| ); |
| debug_assert!(!stack.obligation.predicate.has_escaping_bound_vars()); |
| |
| if let Some(c) = |
| self.check_candidate_cache(stack.obligation.param_env, cache_fresh_trait_pred) |
| { |
| debug!("CACHE HIT: SELECT({:?})={:?}", cache_fresh_trait_pred, c); |
| return c; |
| } |
| |
| // If no match, compute result and insert into cache. |
| // |
| // FIXME(nikomatsakis) -- this cache is not taking into |
| // account cycles that may have occurred in forming the |
| // candidate. I don't know of any specific problems that |
| // result but it seems awfully suspicious. |
| let (candidate, dep_node) = |
| self.in_task(|this| this.candidate_from_obligation_no_cache(stack)); |
| |
| debug!("CACHE MISS: SELECT({:?})={:?}", cache_fresh_trait_pred, candidate); |
| self.insert_candidate_cache( |
| stack.obligation.param_env, |
| cache_fresh_trait_pred, |
| dep_node, |
| candidate.clone(), |
| ); |
| candidate |
| } |
| |
| pub(super) fn assemble_candidates<'o>( |
| &mut self, |
| stack: &TraitObligationStack<'o, 'tcx>, |
| ) -> Result<SelectionCandidateSet<'tcx>, SelectionError<'tcx>> { |
| let TraitObligationStack { obligation, .. } = *stack; |
| let obligation = &Obligation { |
| param_env: obligation.param_env, |
| cause: obligation.cause.clone(), |
| recursion_depth: obligation.recursion_depth, |
| predicate: self.infcx().resolve_vars_if_possible(&obligation.predicate), |
| }; |
| |
| if obligation.predicate.skip_binder().self_ty().is_ty_var() { |
| // Self is a type variable (e.g., `_: AsRef<str>`). |
| // |
| // This is somewhat problematic, as the current scheme can't really |
| // handle it turning to be a projection. This does end up as truly |
| // ambiguous in most cases anyway. |
| // |
| // Take the fast path out - this also improves |
| // performance by preventing assemble_candidates_from_impls from |
| // matching every impl for this trait. |
| return Ok(SelectionCandidateSet { vec: vec![], ambiguous: true }); |
| } |
| |
| let mut candidates = SelectionCandidateSet { vec: Vec::new(), ambiguous: false }; |
| |
| self.assemble_candidates_for_trait_alias(obligation, &mut candidates)?; |
| |
| // Other bounds. Consider both in-scope bounds from fn decl |
| // and applicable impls. There is a certain set of precedence rules here. |
| let def_id = obligation.predicate.def_id(); |
| let lang_items = self.tcx().lang_items(); |
| |
| if lang_items.copy_trait() == Some(def_id) { |
| debug!("obligation self ty is {:?}", obligation.predicate.skip_binder().self_ty()); |
| |
| // User-defined copy impls are permitted, but only for |
| // structs and enums. |
| self.assemble_candidates_from_impls(obligation, &mut candidates)?; |
| |
| // For other types, we'll use the builtin rules. |
| let copy_conditions = self.copy_clone_conditions(obligation); |
| self.assemble_builtin_bound_candidates(copy_conditions, &mut candidates)?; |
| } else if lang_items.discriminant_kind_trait() == Some(def_id) { |
| // `DiscriminantKind` is automatically implemented for every type. |
| candidates.vec.push(DiscriminantKindCandidate); |
| } else if lang_items.sized_trait() == Some(def_id) { |
| // Sized is never implementable by end-users, it is |
| // always automatically computed. |
| let sized_conditions = self.sized_conditions(obligation); |
| self.assemble_builtin_bound_candidates(sized_conditions, &mut candidates)?; |
| } else if lang_items.unsize_trait() == Some(def_id) { |
| self.assemble_candidates_for_unsizing(obligation, &mut candidates); |
| } else { |
| if lang_items.clone_trait() == Some(def_id) { |
| // Same builtin conditions as `Copy`, i.e., every type which has builtin support |
| // for `Copy` also has builtin support for `Clone`, and tuples/arrays of `Clone` |
| // types have builtin support for `Clone`. |
| let clone_conditions = self.copy_clone_conditions(obligation); |
| self.assemble_builtin_bound_candidates(clone_conditions, &mut candidates)?; |
| } |
| |
| self.assemble_generator_candidates(obligation, &mut candidates)?; |
| self.assemble_closure_candidates(obligation, &mut candidates)?; |
| self.assemble_fn_pointer_candidates(obligation, &mut candidates)?; |
| self.assemble_candidates_from_impls(obligation, &mut candidates)?; |
| self.assemble_candidates_from_object_ty(obligation, &mut candidates); |
| } |
| |
| self.assemble_candidates_from_projected_tys(obligation, &mut candidates); |
| self.assemble_candidates_from_caller_bounds(stack, &mut candidates)?; |
| // Auto implementations have lower priority, so we only |
| // consider triggering a default if there is no other impl that can apply. |
| if candidates.vec.is_empty() { |
| self.assemble_candidates_from_auto_impls(obligation, &mut candidates)?; |
| } |
| debug!("candidate list size: {}", candidates.vec.len()); |
| Ok(candidates) |
| } |
| |
| fn assemble_candidates_from_projected_tys( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| debug!("assemble_candidates_for_projected_tys({:?})", obligation); |
| |
| // Before we go into the whole placeholder thing, just |
| // quickly check if the self-type is a projection at all. |
| match obligation.predicate.skip_binder().trait_ref.self_ty().kind() { |
| ty::Projection(_) | ty::Opaque(..) => {} |
| ty::Infer(ty::TyVar(_)) => { |
| span_bug!( |
| obligation.cause.span, |
| "Self=_ should have been handled by assemble_candidates" |
| ); |
| } |
| _ => return, |
| } |
| |
| let result = self |
| .infcx |
| .probe(|_| self.match_projection_obligation_against_definition_bounds(obligation)); |
| |
| if result { |
| candidates.vec.push(ProjectionCandidate); |
| } |
| } |
| |
| /// Given an obligation like `<SomeTrait for T>`, searches the obligations that the caller |
| /// supplied to find out whether it is listed among them. |
| /// |
| /// Never affects the inference environment. |
| fn assemble_candidates_from_caller_bounds<'o>( |
| &mut self, |
| stack: &TraitObligationStack<'o, 'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| debug!("assemble_candidates_from_caller_bounds({:?})", stack.obligation); |
| |
| let all_bounds = stack |
| .obligation |
| .param_env |
| .caller_bounds() |
| .iter() |
| .filter_map(|o| o.to_opt_poly_trait_ref()); |
| |
| // Micro-optimization: filter out predicates relating to different traits. |
| let matching_bounds = |
| all_bounds.filter(|p| p.def_id() == stack.obligation.predicate.def_id()); |
| |
| // Keep only those bounds which may apply, and propagate overflow if it occurs. |
| let mut param_candidates = vec![]; |
| for bound in matching_bounds { |
| let wc = self.evaluate_where_clause(stack, bound)?; |
| if wc.may_apply() { |
| param_candidates.push(ParamCandidate(bound)); |
| } |
| } |
| |
| candidates.vec.extend(param_candidates); |
| |
| Ok(()) |
| } |
| |
| fn assemble_generator_candidates( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| if self.tcx().lang_items().gen_trait() != Some(obligation.predicate.def_id()) { |
| return Ok(()); |
| } |
| |
| // Okay to skip binder because the substs on generator types never |
| // touch bound regions, they just capture the in-scope |
| // type/region parameters. |
| let self_ty = obligation.self_ty().skip_binder(); |
| match self_ty.kind() { |
| ty::Generator(..) => { |
| debug!( |
| "assemble_generator_candidates: self_ty={:?} obligation={:?}", |
| self_ty, obligation |
| ); |
| |
| candidates.vec.push(GeneratorCandidate); |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_generator_candidates: ambiguous self-type"); |
| candidates.ambiguous = true; |
| } |
| _ => {} |
| } |
| |
| Ok(()) |
| } |
| |
| /// Checks for the artificial impl that the compiler will create for an obligation like `X : |
| /// FnMut<..>` where `X` is a closure type. |
| /// |
| /// Note: the type parameters on a closure candidate are modeled as *output* type |
| /// parameters and hence do not affect whether this trait is a match or not. They will be |
| /// unified during the confirmation step. |
| fn assemble_closure_candidates( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| let kind = match self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()) { |
| Some(k) => k, |
| None => { |
| return Ok(()); |
| } |
| }; |
| |
| // Okay to skip binder because the substs on closure types never |
| // touch bound regions, they just capture the in-scope |
| // type/region parameters |
| match *obligation.self_ty().skip_binder().kind() { |
| ty::Closure(_, closure_substs) => { |
| debug!("assemble_unboxed_candidates: kind={:?} obligation={:?}", kind, obligation); |
| match self.infcx.closure_kind(closure_substs) { |
| Some(closure_kind) => { |
| debug!("assemble_unboxed_candidates: closure_kind = {:?}", closure_kind); |
| if closure_kind.extends(kind) { |
| candidates.vec.push(ClosureCandidate); |
| } |
| } |
| None => { |
| debug!("assemble_unboxed_candidates: closure_kind not yet known"); |
| candidates.vec.push(ClosureCandidate); |
| } |
| } |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_unboxed_closure_candidates: ambiguous self-type"); |
| candidates.ambiguous = true; |
| } |
| _ => {} |
| } |
| |
| Ok(()) |
| } |
| |
| /// Implements one of the `Fn()` family for a fn pointer. |
| fn assemble_fn_pointer_candidates( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| // We provide impl of all fn traits for fn pointers. |
| if self.tcx().fn_trait_kind_from_lang_item(obligation.predicate.def_id()).is_none() { |
| return Ok(()); |
| } |
| |
| // Okay to skip binder because what we are inspecting doesn't involve bound regions. |
| let self_ty = obligation.self_ty().skip_binder(); |
| match *self_ty.kind() { |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_fn_pointer_candidates: ambiguous self-type"); |
| candidates.ambiguous = true; // Could wind up being a fn() type. |
| } |
| // Provide an impl, but only for suitable `fn` pointers. |
| ty::FnPtr(_) => { |
| if let ty::FnSig { |
| unsafety: hir::Unsafety::Normal, |
| abi: Abi::Rust, |
| c_variadic: false, |
| .. |
| } = self_ty.fn_sig(self.tcx()).skip_binder() |
| { |
| candidates.vec.push(FnPointerCandidate); |
| } |
| } |
| // Provide an impl for suitable functions, rejecting `#[target_feature]` functions (RFC 2396). |
| ty::FnDef(def_id, _) => { |
| if let ty::FnSig { |
| unsafety: hir::Unsafety::Normal, |
| abi: Abi::Rust, |
| c_variadic: false, |
| .. |
| } = self_ty.fn_sig(self.tcx()).skip_binder() |
| { |
| if self.tcx().codegen_fn_attrs(def_id).target_features.is_empty() { |
| candidates.vec.push(FnPointerCandidate); |
| } |
| } |
| } |
| _ => {} |
| } |
| |
| Ok(()) |
| } |
| |
| /// Searches for impls that might apply to `obligation`. |
| fn assemble_candidates_from_impls( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| debug!("assemble_candidates_from_impls(obligation={:?})", obligation); |
| |
| // Essentially any user-written impl will match with an error type, |
| // so creating `ImplCandidates` isn't useful. However, we might |
| // end up finding a candidate elsewhere (e.g. a `BuiltinCandidate` for `Sized) |
| // This helps us avoid overflow: see issue #72839 |
| // Since compilation is already guaranteed to fail, this is just |
| // to try to show the 'nicest' possible errors to the user. |
| if obligation.references_error() { |
| return Ok(()); |
| } |
| |
| self.tcx().for_each_relevant_impl( |
| obligation.predicate.def_id(), |
| obligation.predicate.skip_binder().trait_ref.self_ty(), |
| |impl_def_id| { |
| self.infcx.probe(|_| { |
| if let Ok(_substs) = self.match_impl(impl_def_id, obligation) { |
| candidates.vec.push(ImplCandidate(impl_def_id)); |
| } |
| }); |
| }, |
| ); |
| |
| Ok(()) |
| } |
| |
| fn assemble_candidates_from_auto_impls( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| // Okay to skip binder here because the tests we do below do not involve bound regions. |
| let self_ty = obligation.self_ty().skip_binder(); |
| debug!("assemble_candidates_from_auto_impls(self_ty={:?})", self_ty); |
| |
| let def_id = obligation.predicate.def_id(); |
| |
| if self.tcx().trait_is_auto(def_id) { |
| match self_ty.kind() { |
| ty::Dynamic(..) => { |
| // For object types, we don't know what the closed |
| // over types are. This means we conservatively |
| // say nothing; a candidate may be added by |
| // `assemble_candidates_from_object_ty`. |
| } |
| ty::Foreign(..) => { |
| // Since the contents of foreign types is unknown, |
| // we don't add any `..` impl. Default traits could |
| // still be provided by a manual implementation for |
| // this trait and type. |
| } |
| ty::Param(..) | ty::Projection(..) => { |
| // In these cases, we don't know what the actual |
| // type is. Therefore, we cannot break it down |
| // into its constituent types. So we don't |
| // consider the `..` impl but instead just add no |
| // candidates: this means that typeck will only |
| // succeed if there is another reason to believe |
| // that this obligation holds. That could be a |
| // where-clause or, in the case of an object type, |
| // it could be that the object type lists the |
| // trait (e.g., `Foo+Send : Send`). See |
| // `compile-fail/typeck-default-trait-impl-send-param.rs` |
| // for an example of a test case that exercises |
| // this path. |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| // The auto impl might apply; we don't know. |
| candidates.ambiguous = true; |
| } |
| ty::Generator(_, _, movability) |
| if self.tcx().lang_items().unpin_trait() == Some(def_id) => |
| { |
| match movability { |
| hir::Movability::Static => { |
| // Immovable generators are never `Unpin`, so |
| // suppress the normal auto-impl candidate for it. |
| } |
| hir::Movability::Movable => { |
| // Movable generators are always `Unpin`, so add an |
| // unconditional builtin candidate. |
| candidates.vec.push(BuiltinCandidate { has_nested: false }); |
| } |
| } |
| } |
| |
| _ => candidates.vec.push(AutoImplCandidate(def_id)), |
| } |
| } |
| |
| Ok(()) |
| } |
| |
| /// Searches for impls that might apply to `obligation`. |
| fn assemble_candidates_from_object_ty( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| debug!( |
| "assemble_candidates_from_object_ty(self_ty={:?})", |
| obligation.self_ty().skip_binder() |
| ); |
| |
| self.infcx.probe(|_snapshot| { |
| // The code below doesn't care about regions, and the |
| // self-ty here doesn't escape this probe, so just erase |
| // any LBR. |
| let self_ty = self.tcx().erase_late_bound_regions(&obligation.self_ty()); |
| let poly_trait_ref = match self_ty.kind() { |
| ty::Dynamic(ref data, ..) => { |
| if data.auto_traits().any(|did| did == obligation.predicate.def_id()) { |
| debug!( |
| "assemble_candidates_from_object_ty: matched builtin bound, \ |
| pushing candidate" |
| ); |
| candidates.vec.push(BuiltinObjectCandidate); |
| return; |
| } |
| |
| if let Some(principal) = data.principal() { |
| if !self.infcx.tcx.features().object_safe_for_dispatch { |
| principal.with_self_ty(self.tcx(), self_ty) |
| } else if self.tcx().is_object_safe(principal.def_id()) { |
| principal.with_self_ty(self.tcx(), self_ty) |
| } else { |
| return; |
| } |
| } else { |
| // Only auto trait bounds exist. |
| return; |
| } |
| } |
| ty::Infer(ty::TyVar(_)) => { |
| debug!("assemble_candidates_from_object_ty: ambiguous"); |
| candidates.ambiguous = true; // could wind up being an object type |
| return; |
| } |
| _ => return, |
| }; |
| |
| debug!("assemble_candidates_from_object_ty: poly_trait_ref={:?}", poly_trait_ref); |
| |
| // Count only those upcast versions that match the trait-ref |
| // we are looking for. Specifically, do not only check for the |
| // correct trait, but also the correct type parameters. |
| // For example, we may be trying to upcast `Foo` to `Bar<i32>`, |
| // but `Foo` is declared as `trait Foo: Bar<u32>`. |
| let upcast_trait_refs = util::supertraits(self.tcx(), poly_trait_ref) |
| .filter(|upcast_trait_ref| { |
| self.infcx |
| .probe(|_| self.match_poly_trait_ref(obligation, *upcast_trait_ref).is_ok()) |
| }) |
| .count(); |
| |
| if upcast_trait_refs > 1 { |
| // Can be upcast in many ways; need more type information. |
| candidates.ambiguous = true; |
| } else if upcast_trait_refs == 1 { |
| candidates.vec.push(ObjectCandidate); |
| } |
| }) |
| } |
| |
| /// Searches for unsizing that might apply to `obligation`. |
| fn assemble_candidates_for_unsizing( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) { |
| // We currently never consider higher-ranked obligations e.g. |
| // `for<'a> &'a T: Unsize<Trait+'a>` to be implemented. This is not |
| // because they are a priori invalid, and we could potentially add support |
| // for them later, it's just that there isn't really a strong need for it. |
| // A `T: Unsize<U>` obligation is always used as part of a `T: CoerceUnsize<U>` |
| // impl, and those are generally applied to concrete types. |
| // |
| // That said, one might try to write a fn with a where clause like |
| // for<'a> Foo<'a, T>: Unsize<Foo<'a, Trait>> |
| // where the `'a` is kind of orthogonal to the relevant part of the `Unsize`. |
| // Still, you'd be more likely to write that where clause as |
| // T: Trait |
| // so it seems ok if we (conservatively) fail to accept that `Unsize` |
| // obligation above. Should be possible to extend this in the future. |
| let source = match obligation.self_ty().no_bound_vars() { |
| Some(t) => t, |
| None => { |
| // Don't add any candidates if there are bound regions. |
| return; |
| } |
| }; |
| let target = obligation.predicate.skip_binder().trait_ref.substs.type_at(1); |
| |
| debug!("assemble_candidates_for_unsizing(source={:?}, target={:?})", source, target); |
| |
| let may_apply = match (source.kind(), target.kind()) { |
| // Trait+Kx+'a -> Trait+Ky+'b (upcasts). |
| (&ty::Dynamic(ref data_a, ..), &ty::Dynamic(ref data_b, ..)) => { |
| // Upcasts permit two things: |
| // |
| // 1. Dropping auto traits, e.g., `Foo + Send` to `Foo` |
| // 2. Tightening the region bound, e.g., `Foo + 'a` to `Foo + 'b` if `'a: 'b` |
| // |
| // Note that neither of these changes requires any |
| // change at runtime. Eventually this will be |
| // generalized. |
| // |
| // We always upcast when we can because of reason |
| // #2 (region bounds). |
| data_a.principal_def_id() == data_b.principal_def_id() |
| && data_b |
| .auto_traits() |
| // All of a's auto traits need to be in b's auto traits. |
| .all(|b| data_a.auto_traits().any(|a| a == b)) |
| } |
| |
| // `T` -> `Trait` |
| (_, &ty::Dynamic(..)) => true, |
| |
| // Ambiguous handling is below `T` -> `Trait`, because inference |
| // variables can still implement `Unsize<Trait>` and nested |
| // obligations will have the final say (likely deferred). |
| (&ty::Infer(ty::TyVar(_)), _) | (_, &ty::Infer(ty::TyVar(_))) => { |
| debug!("assemble_candidates_for_unsizing: ambiguous"); |
| candidates.ambiguous = true; |
| false |
| } |
| |
| // `[T; n]` -> `[T]` |
| (&ty::Array(..), &ty::Slice(_)) => true, |
| |
| // `Struct<T>` -> `Struct<U>` |
| (&ty::Adt(def_id_a, _), &ty::Adt(def_id_b, _)) if def_id_a.is_struct() => { |
| def_id_a == def_id_b |
| } |
| |
| // `(.., T)` -> `(.., U)` |
| (&ty::Tuple(tys_a), &ty::Tuple(tys_b)) => tys_a.len() == tys_b.len(), |
| |
| _ => false, |
| }; |
| |
| if may_apply { |
| candidates.vec.push(BuiltinUnsizeCandidate); |
| } |
| } |
| |
| fn assemble_candidates_for_trait_alias( |
| &mut self, |
| obligation: &TraitObligation<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| // Okay to skip binder here because the tests we do below do not involve bound regions. |
| let self_ty = obligation.self_ty().skip_binder(); |
| debug!("assemble_candidates_for_trait_alias(self_ty={:?})", self_ty); |
| |
| let def_id = obligation.predicate.def_id(); |
| |
| if self.tcx().is_trait_alias(def_id) { |
| candidates.vec.push(TraitAliasCandidate(def_id)); |
| } |
| |
| Ok(()) |
| } |
| |
| /// Assembles the trait which are built-in to the language itself: |
| /// `Copy`, `Clone` and `Sized`. |
| fn assemble_builtin_bound_candidates( |
| &mut self, |
| conditions: BuiltinImplConditions<'tcx>, |
| candidates: &mut SelectionCandidateSet<'tcx>, |
| ) -> Result<(), SelectionError<'tcx>> { |
| match conditions { |
| BuiltinImplConditions::Where(nested) => { |
| debug!("builtin_bound: nested={:?}", nested); |
| candidates |
| .vec |
| .push(BuiltinCandidate { has_nested: !nested.skip_binder().is_empty() }); |
| } |
| BuiltinImplConditions::None => {} |
| BuiltinImplConditions::Ambiguous => { |
| debug!("assemble_builtin_bound_candidates: ambiguous builtin"); |
| candidates.ambiguous = true; |
| } |
| } |
| |
| Ok(()) |
| } |
| } |